Co-existence of a huge pseudocyst and mucinous cystadenoma: report of a case and the value of magnetic resonance imaging for differential diagnosis.

Co-existence of a pancreatic pseudocyst and a neoplastic cyst is rare and their differential diagnosis is difficult if the patient has an atypical history as well as subclinical symptoms. The formation of a pseudocyst under such circumstances is usually the result of downstream ductal obstruction by the neoplasm. Two large cysts were found in a 43-year-old woman who had symptoms of gastric outlet obstruction that were the result of external compression by one of the cysts. Magnetic resonance imaging was superior to computed tomography, discriminating between the internal contents and surrounding tissue of the two cysts, enabling the correct preoperative diagnosis of a pseudocyst co-existing with a mucinous cystadenoma to be made. It was most unusual for the pseudocyst to be located downstream of the mucinous tumour, ruling out ductal obstruction by the tumour in its pathogenesis. A possible explanation for the pseudocyst formation in this case was pancreatic juice accumulation in the space of the lesser sac after pancreatic parenchymal destruction by the mucinous tumour.